Disturbance and productivity as codeterminants of stream food web complexity in the Arctic
Limnol. Oceanogr., 58(6), 2013, 2158-2170 | DOI: 10.4319/lo.2013.58.6.2158
ABSTRACT: Disturbance and productivity are potentially interacting factors often thought to underlie the complexity of aquatic food webs. We tested predictions about the effects of disturbance (bed movement, total water column freezing) and productivity (as indicated by primary consumer biomass) on the structure of 19 stream food webs in arctic Alaska. We predicted that food webs subject to high levels of disturbance would have low connectance, low linkage density, and short food chains, while food webs of streams with more benign disturbance regimes would be more complex (i.e., a test of the “dynamic stability hypothesis”). We further predicted that food chain length would increase with productivity (i.e., testing the “resource-availability hypothesis”). Connectance and linkage density were negatively related to bed movement but not to freezing. Food chain length was related to freezing but not to bed movement or productivity. The relationships among food chain length, freezing, and productivity were driven by the occurrence of fishless streams, which all froze during winter. Streams containing fish had longer food chains than fishless streams, and food chain length was positively related to productivity only when fishless streams were removed from analyses. Our results show that disturbance and productivity are codeterminants of stream food web complexity in the Arctic. Our data further suggest that colonization dynamics are an important factor controlling food web structure, highlighting the importance of idiosyncratic habitat and life history related factors that are often overlooked in theoretical studies.